Many types of fluids have been used in drilling oil and gas wells. These fluids are generally known as drilling fluids or muds. There are two major types of drilling fluids utilized in drilling an oil well; one is a water-based mud in which the fluid is water. If oil is emulsified into the water, it is known as an oil-in-water emulsion. The second type is an oil-based mud in which the fluid is oil with water or any other aqueous fluid emulsified in the oil, therefore known as a water-in-oil emulsion. The selection of drilling fluid involves a careful balance of both the good and bad characteristics of such fluids in a particular application, the type of well to be drilled and the characteristics of the oil or gas field in which the well is to be drilled.
Drilling fluids provide several important functions, including lubricating the drill bit, establishing a fluid counter-pressure to prevent high-pressure oil, gas and/or water formation fluids from entering the well prematurely, thus preventing the collapse of the uncased wellbore. Drilling muds also remove drill cuttings from the drilling area and transport them to the surface where they can be separated. At the same time, the drilling fluid is expected to cool and clean the drill bit and reduce friction between the drill string and the sides of the hole. The drilling fluid should also form a thin, low-permeability filter cake that seals openings in formations penetrated by the drill bit and reduce the unwanted influx of formation fluids from permeable rocks. The uses, composition and properties of oil well drilling fluids are described in “Composition and Properties of oil well/drilling Fluids” by Gray and Darley, published by Gulf Publishing Company 1988, which is incorporated as a reference in this disclosure.
Water-based muds are preferred over oil-based muds due to lower cost and better environmental profiles. However, oil-based muds have better drilling performance characteristics and are especially preferred when drilling water sensitive formations. Also, oil-based muds have better lubricating properties and higher temperature stability as compared to water based muds.
Oil-based muds contain a small amount of water which is emulsified in oil. This emulsion is known as water-in-oil or invert emulsion drilling fluid commonly containing at least 5% and up to as much as 50%, by volume of water or aqueous brine (salt solution). The water is dispersed in invert emulsions as aqueous droplets throughout a continuous (i.e., external) oil or synthetic oil phase, which may contain diesel fuel or other liquid hydrocarbon mixtures (e.g., olefinic and/or paraffinic species in the C16-C18 range). The aqueous dispersed (i.e., internal) phase is normally a saline, aqueous solution (e.g., a chloride containing brine solution, such as a 30% calcium chloride brine).
Invert emulsion drilling fluids typically result from mixing hydrocarbon oil with water or brine under high shear conditions and in the presence of a suitable emulsifier. A stable emulsion is obtained when there is no distinct layer of oil and water in the fluid mixture when agitation or mixing is stopped and there is uniform dispersion of water droplets throughout the oil phase. The emulsifier is required not only to form a stable dispersion of water droplets in the oil phase, but also to maintain any solids such as weighting material additives (e.g., barites) or drill cuttings in an oil-wet state. In addition to these weighting materials, various other drilling fluid additives are often incorporated into invert emulsion systems to enhance the drilling performance characteristics of drilling fluids. These additives include organo clays and other materials that increase fluid viscosity, fluid loss control additives to reduce fluid loss to the surrounding formation, oil-wetting agents to keep solids and drill-string in oil-wet state, rheology modifiers to help suspend drill cuttings and maintain proper rheology profile and lubricants to impart better lubricant properties to the drilling fluid.
With respect to emulsifiers and other additives used in invert emulsion drilling fluids, various liquid and solid formulations are described in the art.
U.S. Pat. No. 2,946,746 describes water-in-oil type emulsions comprising a polyamide emulsifying agent which may be prepared by reacting a polyethylene polyamine with a monobasic fatty acid in sufficient quantity to react with all of the amino groups of the polyethylene polyamine, thereby converting them to fatty acid amide groups.
U.S. Pat. No. 4,233,162 describes an emulsifier composition comprising a fatty acid amide, oleic acid, dimerized oleic acid and a surfactant dispersant that may be a mixture of a second type of fatty acid amide and waste lignin liquor derived from pulping wood.
U.S. Pat. No. 4,374,737 describes a drilling fluid composition that uses a non-polluting oil (e.g., vegetable or mineral oil) and a concentrate that is added in an amount of about 3% by weight. The concentrate consists essentially of a diethanolamide, a tall oil fatty acid and an imidazoline/amide mixture. Water may be added to the composition to provide an invert emulsion system.
U.S. Pat. No. 4,508,628 describes an invert oil emulsion drilling fluid containing a non-toxic biodegradable oil, an aqueous phase and an emulsifier. The drilling fluid has defined characteristics which provide low viscosity at the high shear rates imparted to the fluid during drilling.
WO 89/11516 describes an oil based well working fluid comprising a hydrocarbon drilling oil in combination with a sodium, calcium, or magnesium brine. The emulsifier used comprises the reaction product of an amide-amine or a hydroxyalkyl amide with a dicarboxylic acid or an acid anhydride.
U.S. Pat. Nos. 4,956,104; 5,045,593; and related patents describe the use of organophilic derivatives of water soluble polymers, prepared by reacting the polymer with a phosphatide such as lecithin, as fluid loss additives for oil based well working fluids.
U.S. Pat. No. 5,096,883 describes a non-toxic drilling fluid which can be an emulsion of a base oil, an aqueous phase and an emulsifying agent. The base oil consists essentially of branched-chain paraffins, which may contain ester functionalities and has a number of defined properties. The drilling fluid avoids the use of aromatics, which are said to have potential environmental consequences.
U.S. Pat. No. 6,461,999 describes the use of lubricating additives for drilling fluids which avoid the need for certain undesirable emulsifiers, surfactants, solvents, or dispersants. The additives are prepared by steam jet cooking a mixture of starch, water and a lubricant such as a polyalkylene.
U.S. Pat. No. 6,620,770 and related U.S. Patent Application Publication Nos. 2004/0171498; 2005/0137093; and 2005/0037929 describe emulsion stability and filtration control additives for invert emulsion drilling fluids. The additives are prepared by blending a carboxylic acid terminated polyamide with the Diels-Alder reaction product of dienophiles (e.g., carboxylic acids, polycarboxylic acids, or acid anhydrides) and a mixture of fatty acids and resin acids.
U.S. Pat. No. 4,544,756 describes manufacturing of yet another liquid invert emulsifier composition consist of zwitter ionic 2-alkyl imidazoline prepared from tall oil fatty acid, polyalkelene poly amine and cis-unsaturated dicarboxylic acid.
Most of the additives known in the art, especially invert emulsifiers and wetting agents used in oil based muds are liquids. At extremely low temperature conditions, it is difficult to keep these liquid additives in a flowable form. Many a time it becomes impossible to use such liquid products in areas where the temperatures are sub-zero.
Therefore, liquid drilling additives use carrier solvents to improve flow properties for their successful application in real field application. However, the carrier solvents not only impart cost, logistic and environmental concerns but they are detrimental to the performance characteristics of the drilling fluids as well.
Along with these low temperature conditions, the availability of limited space at some well sites, such as on offshore platforms and increasing costs of transport of materials to a well site is a grave concern. Thus there is industry wide interest in drilling fluid compositions that can be formulated and maintained (i.e., stored) with minimal or fewer quantities of solvent and other additives.
Therefore it is desirable to have drilling fluid additives which are free-flowing powders and can be used at well sites regardless of temperature conditions and which are free of carrier solvents to improve the environmental and performance characteristics of the additives.